Many applications include a power transistor that, upon being turned on, provides supply voltage from a voltage source to a load. An output capacitor may be coupled to or across the load. The output capacitor may help filter noise on the supply voltage to the node. Further, the output capacitor can be charged by the voltage source and then used to provide current to the load in the event of a momentary outage of the supply voltage.
The power transistor dissipates power during the time the output capacitor is being charged. During the output capacitor charge cycle, the power transistor can experience a voltage drop across its current terminals (e.g., drain and source) of tens of volts (e.g., 60 V) and high current through the transistor to the output capacitor of, for example, 2 A. The example of a 60 V drop across the power transistor at 2 A of charge current means that the power transistor in this example will dissipate 120 watts. At that power dissipation level, the internal core temperature of the power transistor will very quickly increase to a dangerous level (dangerous in that the temperature of the power transistor may exceeds its rated temperature value and violate its thermal safe operating area boundary and damage the power transistor).